Pistons for internal combustion engines



June 27, 1967 I J. L. HEPWORTH 3,

PISTONS FOR INTERNAL COMBUSTION ENGINES Filed Oct. 8, 1964 4 Sheets-Sheet l W "6a 6a In venlor J'.L. HEPwoa-ru By MIMI, Wm M;

June 27, 1967 J. 1.. HEPWORTH 3,327,594

PISTONS FUR INTERNAL COMBUSTION ENGINES Filed Oct. 8, 1964 4 Sheets-Sheet 2 Fig.3 1/70,,

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Inventor I. L. EPMIORTH J m 1967 J. L. HEPWORTH PISTONS FOR INTERNAL COMBUSTION ENGINES 4 Sheets-Sheet 5 Filed Oct. 8, 1964 Fig.8

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lnvenlor 'I- L. EPWORT B umxwhfiwb 4mg June 27, 1967 J. 1.. HEPWORTH PISTONS FOR INTERNAL COMBUSTION ENGINES 4 Sheets-Sheet 4 Filed Oct. 8, 1964 lnvenlor J. L. HEpwaR-ra m'n ttorneys United States Patent 3,327,594 PISTGNS FOR INTERNAL COMBUSTION ENGHNES J ack Lyndhurst Hepworth, Illkley, Yorkshire, England, as-

signor to Hepworth and Grandage Limited, Bradford, England, a British company Filed Oct. 8, 1964, Ser. No. 402,567 13 Claims. (Cl. 92-228) The present invention relates to pistons for internal combustion engines, and in particular to pistons cast from a metal, for example, a light alloy, which has a higher 00- eflicient of expansion than the metal of the cylinders within which the pistons operate, and which are provided with metal inserts for controlling the radial expansion of the thrust faces of the piston wall.

According to the present invention, an internal combustion engine piston includes a gudgeon pin boss and a side wall having diametrically opposed thrust faces displaced circumferentially from the axis of the gudgeon pin boss, wherein at least two inserts having different rates of thermal expansion extend generally diametrically between the thrust faces to form a direct tie therebetween at different levels with respect to the longitudinal axis of the piston.

The invention also consists in an internal combustion engine piston having a crown, a gudgeon pin boss located on the underside of the crown on or adjacent the axis of the piston, and a side wall having diametrically opposed thrust faces displaced circumferentially from the axis of the gudgeon pin boss, and at least two inserts, each of a metal having a lower coefiicient of expansion than that of the metal of the piston, which are disposed at different levels with respect to the longitudinal axis of the piston, and which extend generally diametrically between, and are embedded in, the thrust faces to form a direct tie therebetween, at least that insert most adjacent to the crown engaging said gudgeon pin boss.

In order that the invention may be more readily understood, reference will now be made to the accompanying drawings in which:

FIGURES l and 2 are vertical cross-sections of a piston according to one embodiment of the invention, taken in planes extending at right angles and parallel to the axis of the gudgeon pin boss respectively.

FIGURE 3 is a transverse section of the piston shown in FIGURES l and 2, taken through the axis of the gudgeon pin boss,

FIGURES 4 and 5 are perspective views of the inserts shown in FIGURES 1 to 3,

FIGURES 6 and 7, are perspective views of modified outer ends of two inserts,

FIGURES 8 and 9 are vertical cross-sections of piston according to another embodiment, taken in planes extending at right angles and parallel to the axis of the gudgeon pin boss respectively, and

FIGURES l0 and 11 are vertical and transverse crosssections of pistons according to a further embodiment.

Referring to FIGURES 1 to 3, an internal combustion engine piston, cast from a light alloy, consists of a side Wall 1 closed at its upper end by a crown 2 having a gudgeon pin boss 3, cast integrally with the centre of the underside thereof. This central boss 3 is bored at 4 to receive a gudgeon pin (not shown) on which a bifurcated small end of a connecting rod (not shown) is journalled.

3,327,594 Patented June 27, 1967 A pair of outer gudgeon pin bosses 5 are cast integrally with the side wall 1, which are bored at 6 to receive the outer ends of the gudgeon pin to reduce the bending and shear forces acting thereon. An annular groove 6a is formed adjacent the outer end of each bore 6 to receive a circlip (not shown) which axially locates the gudgeon pin.

The piston is provided with a pair of inserts, namely upper and lower inserts 7' and 7", disposed in a common plane coincident with the longitudinal axis of the piston. Each insert is stamped or otherwise formed to the configuration shown in FIGURES 4 and 5 from a metal which has a lower coeflicient of expansion than that of the alloy from which the piston is cast, and the upper insert 7 is formed from a metal which has a different, for example, a lower, coeflicient of expansion than that of the lower insert 7". The inserts 7' and 7", which are diametrically arranged in a common plane at right angles to the axis of the bores 4 and 6, are embedded at their centres in the central boss 3, respectively above and below the axis of the bosses 3 and 5, and at their outer ends in the portions of the wall, the outer surfaces of which constitute the two opposed thrust faces 10 of the piston, to provide a direct tie therebetween. The outer ends of the inserts are formed with oppositely and circumferentially extending flanges 7a to provide a positive anchorage in the wall 1, and the wall 1 is strengthened in the region of the flanges 7a by axially extending ribs lb.

As will be seen from FIGURES 4 and 5, the inserts 7 and 7" are provided with clearance recesses 7b for the gudgeon pin, and the insert 7' is provided with a perforation 7c. The insert 7 may, however, take the form of a plain plate, imperforate except for the gudgeon pin clearance recess 75. The lower edge 72 of the lower insert 7" is concave to provide clearance in the region of the central boss 3 for movement of the connecting rod (not shown), whilst providing the maximum anchorage in the piston wall 1.

The anchoring flanges at the outer ends of one or both of the inserts may be modified as shown in FIGURES 6 and 7. In FIGURE 6, each flange is divided into portions 7g which project alternately in opposite circumferential directions, whilst in FIGURE 7 each end of the insert is formed with a continuous flange 711 which extends in both circumferential directions.

FIGURES 8 and 9 illustrate a light alloy piston provided with inserts 7' and 7" similar to those shown in the preceding figures. In this embodiment, however, the lower half of the central gudgeon pin boss 3 is omitted. By dispensing with this lower half of the boss 3, improved lubrication of the gudgeon pin and reduced Weight are obtained without impairing performance. The upper half of the boss 3 still provides the necessary firing load support for the gudgeon pin, but the much lower inertia forces can adequately be accommodated by the outer bosses 5.

FIGURES l0 and 11 show a particularly advantageous embodiment of solid skirt pistons, similar to those previously described, but in which a pair of part-circumferentially extending thermal isolating slots 8 are provided in the lowermost piston ring groove.

When a light alloy piston as hereinbefore described is assembled in an internal combustion engine, the heat generated during operation of the engine tends to cause the piston to expand radially at a higher rate than the cylinder within which it is reciprocating. However, since the inserts form a direct tie between the opposed thrust faces of the piston wall 1, the inserts restrict the radial expansion of the thrust faces by virtue of the lower rate of expansion of the inserts.

The expansion of a piston during operation thereof, is not constant over its entire length, due to variations in the thickness of the piston wall or skirt and/or in the operating temperature thereof along the length of the piston. By selecting materials for the inserts which have different coefficients of thermal expansion it is possible to balance the varying rate of expansion of the piston and thereby obtain a more accurate control over the skirt expansion. In particular, it is possible to design a piston with a minimum working clearance which will be maintained at working and ambient temperatures and also throughout the engine temperature range. Moreover, it is also possible to employ a simpler skirt shape, for example, the skirt may be ground parallel along its length instead of form ground.

It will be understood that various modifications may be made without departing from the scope of the present invention. For example, in the embodiments described with reference to FIGURES 1 to 3, and 11, the outer gudgeon pin bosses may be omitted so that the gudgeon pin is supported solely by the central boss. One or more apertures may be provided in the piston wall to enable the gudgeon pin to be assembled in and removed from the central boss. Alternatively, the central boss may be omitted, in which case at least the lower insert passes between the two portions of the divided or forked connecting rod small end journal without being supported at its centre.

Moreover, instead of arranging the pairs of inserts diametrically, two or more pairs of inserts may be provided which extend parallel to the centre line or axis of the piston, their spacing being governed by the width of the central boss. These pairs of inserts may extend parallel to each other, or may be disposed at a slight angle to each other. They may also be disposed at an angle to the piston axis instead of parallel thereto.

Instead of providing a pair of inserts as shown in the drawings, three or more inserts may be provided, preferably disposed diametrically in a common plane coincident with the piston axis.

The pistons hereinbefore described have the advantage that, due to the small end journal of the engine connecting rod being located on each side of the boss 3, instead of centrally as in conventional pistons, it is possible to have a direct tie between the two opposing thrust faces of the piston wall.

I claim:

1. An internal combustion engine piston, including a crown, at least one gudgeon pin boss, and a side wall depending from the crown and having diametrically opposed thrust faces displaced circumferentially from the axis of the gudgeon pin boss, wherein at least two inserts, each, of a metal having a lower coefficient of expansion than that of the metal of the piston, extend generally diametrically between the thrust faces to form a direct tie therebetween at different levels with respect to the longitudinal axis of the piston, said inserts being adapted to exert restraints on said thrust faces such that the thermal expansion per unit temperature rise of said thrust faces is less in the region of the upper end of the side wall adjacent the crown than in the region of the lower end of the side wall remote from the crown.

2. A piston as claimed in claim 1, wherein the insert most adjacent to the crown has a coefficient of thermal expansion which is lower than that of the or each other insert.

3. An internal combustion engine piston having a crown, a gudgeon pin boss located on the underside of the crown on or adjacent the axis of the piston, and a side wall having diametrically opposed thrust faces displaced circumferentially from the axis of the gudgeon pin boss, at least two inserts each of a metal having a lower coeflicient of thermal expansion than that of the metal of the piston, which are disposed at different levels with respect to the longitudinal axis of the piston, and which extend generally diametrically between, and are embedded in, the thrust faces to form a direct tie therebetween, at least that insert most adjacent to the crown engaging said gudgeon pin boss.

4. A piston as claimed in claim 3, wherein at least the uppermost insert is embedded at or adjacent its center in the gudgeon pin boss.

5. A piston as claimed in claim 3, wherein at least one generally axially and circumferentially extending flange is provided at each radially outer end of each insert, embedded in the side wall in the region of a thrust face of the piston, the side wall being strengthened in the region of said flanges by axially extending ribs.

6. A piston as claimed in claim 3, wherein a gudgeon pin boss is provided in each side wall of the piston on each side ofthe central gudgeon pin boss to receive and locate the outer ends of a gudgeon pin.

7. A piston as claimed in claim 6, wherein at least a part of the region of said central gudgeon pin boss disposed below the axis thereof is omitted.

8. An internal combustion engine piston including a gudgeon pin boss, and a side wall having diametrically opposed thrust faces displaced circumferentially from the axis of the gudgeon pin boss, wherein at least two inserts having different coeflicients of thermal expansion extend generally diametrically between the two thrust faces to form a direct tie therebetween at different levels with respect to the longitudinal axis of the piston.

9. A piston as claimed in claim 8, wherein one of the inserts is disposed generally above the axis of the gudgeon pin boss and the other is disposed generally below said axis.

10. A light alloy piston including a piston crown, a side wall integral with and depending from said crown, a pair of diametrically opposed, axially aligned, outer gudgeon pin bosses integral with said side wall, a central gudgeon pin boss integral with and depending from the underside of said crown, disposed between and axially aligned with said outer gudgeon pin bosses, diametrically opposed thrust faces externally of said side wall and displaced circumferentially from the common axis of said gudgeon pin bosses, first and second metal inserts disposed generally diametrically in a common plane coinci-. dent with the longitudinal axis of the piston having coefficients of thermal expansion lower than that of the alloy of the piston but different from each other, at least one generally axially and circumferentially extending flange at each radially outer end of each insert, embedded in said side wall in the region of thrust face, with the flanges of said first insert embedded in said side wall at positions nearer to the piston crown than, and spaced from, the flanges of said second insert, whereby said inserts form a direct tie between said opposed thrust faces at different levels with respect to the longitudinal axis of the piston, the side wall being strengthened in the region of said flanges by axially extending ribs, and the central portion of said first insert being embedded in said central gudgeon pin boss.

11. A piston according to claim 10, wherein the central portion of said second insert is embedded in said central gudgeon pin boss.

12. A piston according to claim 10, wherein the portion of the central gudgeon pin boss below the axis thereof is omitted.

13. A solid skirt piston according to claim 10, including a pair of part-circumferentially extending slots formed in the side wall of the piston and thermally isolating said opposed thrust faces from said crown.

(References 011 following page) Referencs Cited 2,284,152 5/1942 Kno w 92228 12 1:1 1 S PATENTS 29 156 5 FOREIGN PATENTS 3/1938 Teetor 92228 5 6861883 7/1930 France- 33:33; MARTIN P. SCHWADRON, Primary Examiner. 11/1940 Berry 92, 229 G. N. BAUM, Assistant Examiner. 

1. AN INTERNAL COMBUSTION ENGINE PISTON, INCLUDING A CROWN, AT LEAST ONE GUDGEON PIN BOSS, AND A SIDE WALL DEPENDING FROM THE CROWN AND HAVING DIAMETRICALLY OPPOSED THRUST FACES DISPLACED CIRCUMFERENTIALLY FROM THE AXIS OF THE GUDGEON PIN BOSS, WHEREIN AT LEAST TWO INSERTS, EACH, OF A METAL HAVING A LOWER COEFFICIENT OF EXPANSION THAN THAT OF THE METAL OF THE PISTON, EXTEND GENERALLY DIAMETRICALLY BETWEEN THE THRUSH FACES TO FORM A DIRECT TIE THEREBETWEEN AT DIFFERENT LEVELS WITH RESPECT TO THE LONGITUDINAL AXIS OF THE PISTON, SAID INSERTS BEING ADAPTED TO EXERT RESTRAINST ON SAID THRUST FACES SUCH THAT THE THERMAL EXPANSION PER UNIT TEMPERATURE RISE OF SAID THRUST FACES IS LESS IN THE REGION OF THE UPPER END OF THE SIDE WALL ADJACENT THE CROWN THAN IN THE REGION OF THE LOWER END OF THE SIDE WALL REMOTE FROM THE CROWN. 